Summary:
The copper-cobalt minerals hosted in rocks of the Neoproterozoic Katangan Basin in the Central African copper belt metallogenic province of the DRC are a classic example of (low energy) sediment-hosted stratiform copper (SSC) ore system deposits. These deposits are economically significant, as they account for approximately 25% of the world’s copper production and known Mineral Reserves being second only to porphyry copper deposits in terms of copper production and the most important global cobalt resource.
The copper-cobalt deposits contained in a sedimentary series of rocks are known as the Mines Group in the Katanga sequence and the Roan Group in Zambia. The sediments are shallow-water shales, dolomitic shales, reefal dolomites and possible evaporitic lagoonal mudstones, formed on a platform marginal to a subsiding basin. The rocks are exposed in a series of tightly folded and thrusted anticlines and synclines, which generally trend east-west or southeast and are often overturned to the north. In spite of this deformation overprint, the mineralized zones, although sometimes lenticular along strike and down dip, as well as showing local diapiric forms, display remarkable large-scale continuity within the Mines Group.
With the exception of Tilwezembe OP, all of the mineralized properties of KCC are localized within the Kolwezi Nappe, a northeast striking synclinal basin with major and minor axes of approximately 20 km and 10 km respectively. Tilwezembe OP is located about 20 km to the east of Kolwezi.
Within the Kolwezi Nappe, each of the project areas, T17 Mine, Kananga OP, KTO UG, KOV OP and Mashamba East OP contain fragments with intact successions of Series Des Mines lithologies, which host the copper and cobalt mineralization. The fragments are often structurally complex, being tightly folded and exhibiting variable strikes and dips both within individual rafts and between neighbouring rafts.
T17 Mine
The T17 West is described as dismembered structurally complex packages, which belong to the southern flank of a synclinal fold that extends 2.6 km and is overturned towards the north. Faulting is assumed to be the predominant process in the deformation and dismemberment of the deposit.
Tilwezembe OP
The mineralized zone of Tilwezembe is located in a northeast-southwest anticlinal structural lineament, which extends further to the east where known copper and cobalt deposits exist (Kisanfu, Myunga, Kalumbwe and Deziwa). Strongly brecciated siliceous dolomites and shales of the Mwashya Formation (or R4) dominate with interstitial bands of haematite and oolites. The strata strike almost east-west and dips at about 45° to the south.
Kananga OP
The Kananga orebody outcrops and forms a ridge with a north-northeast strike. The ridge falls quite rapidly towards the south and has been cut to form part of the embankment for the Lobito railway line, which runs parallel to the ridge and 10 m to 20 m away from it for most of the strike length of the orebody. GCM interpretations indicate that Kananga is the northern limb of the Kananga Dilala syncline, which plunges to the south.
KOV OP
The KOV OP deposit can be sub-divided into five main fragments within the KCC concession. These fragments can be classified as rafts of the Lower Roan lithologies which are separated by faults and/or RAT Lilas waste intrusions. The KOV fragments as follows:
- KTE: Can be divided into three sub-fragments; KTEA forms a broad syncline dipping at approximately 40° north, KTEB lies below KTEA and dips approximately 30° north, whilst KTEC lies to the east of the KTEB and is sub-vertical;
- Oliveira: A broad open syncline with the northern limb dipping 5° to the southwest and the southern limb dipping 25° to the northwest;
- Virgule: A rectangular fragment which is faulted in the west, appearing as a ‘trouser leg” shape. It is dipping 20° to the southwest;
- Variante: Forms a rough L-shape plane, with the eastern portion steeply dipping 70° to the north, shallow dipping 20° to the west;
- FNSR: An over turned fragment, rectangular fragment which is dipping 25° to the southwest.
Mashamba East Mine
The Mashamba East has an intact succession of Series de Mines lithologies, which host the copper and cobalt mineralization. Structurally, the lithologies of the Mashamba East strike to the northeast and dip 20° to the northwest in the west and wraps around to strike almost north-south and dip 35° to the east in the eastern portion of the property.
KTO UG
KTO UG operations extract mineralized copper ore from the Kamoto deposit, which is differentiated from KTE, predominantly mined in the KOV OP, but contains the same lithologies. The KTO UG is subdivided into five fragments as follows:
- Principal: forms a rough L-shape syncline, flat lying to gently dipping (up to 8° to the north) in the central and northern areas and becoming steeper (15° to 25°) towards the east and west flanks. The steeply dipping area to the south is sub-vertical in places and is separated from the flatter dipping area by structurally complex zones and RAT Lilas waste intrusions;
- Etang South: forms a broad open synform dipping 25° to 35° to the east on an approximate north northwest strike;
- Etang North: forms a roughly rectangular slab dipping 35° to 55° to the east on an approximate northnortheast strike. It extends below the Principal fragment in the north;
- Ecaille Renversee: a small reversed fragment between Principal and Etang North; and
- Pringle: forms a moderately open synform dipping 35° to 55° to the southeast on an approximate north strike.
Primary mineralization, in the form of sulphides, within the Lower Roan is associated with the DSTRAT and RSF for the OBI and the SDB and SDS for the OBS and is thought to be syn-sedimentary in origin. Typical primary copper sulphide minerals are bornite, chalcopyrite, chalcocite and occasional native copper while cobalt is in the form of carrolite. The mineralization occurs as disseminations or in association with hydrothermal carbonate alteration and silicification. Supergene mineralization is generally associated with the levels of oxidation in the subsurface sometimes deeper than 100 m below surface. The most common secondary supergene minerals for copper and cobalt are malachite and heterogenite.
The RSC, a lithological unit stratigraphically intermediate between the OBS and OBI host rocks , contains relatively less copper mineralization. The RSC contains appreciable copper mineralization near the contacts with the overlying SDB formation and the underlying RSF formations. The middle portion of the RSC, considered to be “sterile” by GCM, normally contains relatively less copper mineralization and was historically not sampled. KCC currently samples the entire RSC. The mineral potential of the RSC is less well known than that of other formations.
The RSC has been observed to be well mineralized in supergene cobalt hydroxide, heterogenite, which occurs as vug infillings, especially near the surface.